More specifically this invention relates to: (a) methods for the preparation of solutions and sols derived from alkoxide precursors that are particularly reactive and useful for preparing magnetic and/or magnetoresistive ceramics; (b) the novel alkoxide-based precursors; (c) methods for converting the solutions and sols into manganite ceramics, including coatings and films, particularly thin films; (d) the novel ceramics, coatings and films derived from these precursors, (e) methods for constructing manganite ceramic materials and devices; and (f) the novel materials and devices produced by these methods. Perovskite manganite ceramic materials typically exhibit magnetoresistance properties useful for integration into hybrid microelectronics as solid-state sensors and nonvolatile memory elements. Changes in electrical resistance caused by external electrical or magnetic fields or by temperature changes allow manganite ceramics, when based on the lanthanide series and doped with divalent cations, to sense magnetic fields and heat. As a result, the perovskite ceramics can enhance magnetic recording systems as well as thermal and infrared detectors.
Manganite ceramics can also be based on certain non-lanthanide elements, provided the non-lanthanide elements have a chemistry similar to the “true lanthanides,” and are capable of forming +3 ion having a size similar to a “true lanthanide” +3 ion. Yttrium is one example of such a non-lanthanide element having these properties that can be used to form the novel ceramics described in more detail below. As used herein, the term Ln represents elements from the lanthanide series and other non-lanthanide elements having the features described above.
Some of the techniques used to prepare manganite ceramic devices include chemical vapor deposition and sputtering, spin-coating of chemical solutions, laser ablation, electron beam deposition and ion beam deposition. Of these methods spin coating generally requires less capital investment, is less expensive to operate and has fewer restrictions as to size and shape of the substrate coated. Industrial spin-coating methods have several requirements. A superior precursor solution system used for a spin-coating process should: (1) be derived from available starting materials, (2) not contain particulate matter, (3) have sufficient shelf life to allow for processing, (4) be capable of bonding to the substrate, (5) have the proper rheology to form a uniform coating, (6) be highly reactive during the coating process so that a gel is formed preserving the coating's uniformity, and (7) provide a gel having sufficient reactivity to provide a manganite ceramic coating of uniform thickness without breaks or defects over the coated area without requiring temperatures high enough to damage the desired substrate. Aspects of this invention, the novel precursor solutions containing sols, methods for preparing and converting the precursor solutions into perovskite ceramics address these needs.